This invention relates to cleaning apparatus for printing presses and, in particular, to a dry vacuum apparatus for cleaning a blanket cylinder in an offset printing press without interrupting or slowing the operation of the press.
Offset printing, in comparison with the letterpress method of printing, has become the predominant printing method in the newspaper publishing industry. This is due in part to the increased sharpness of the printed images and the ability to print on less even surfaces than are required by the letterpress method. Also, another important factor in the popularity of offset printing is the lower cost of the printing plates used with offset presses.
Offset printing presses typically employ a blanket cylinder, that is to say, a rubber cylinder or a rubber-covered cylinder, for the purposes of receiving inked images from a printing plate. The inked images are then offset onto paper passed between the blanket cylinders or an impression cylinder. Continuous printing is made possible by wrapping a printing plate or a plurality of printing plates around the surface of a plate cylinder designed for rotation in contact with the blanket cylinder.
In operating blanket-to-blanket presses, a web of paper passes between two blanket cylinders mounted such that one blanket cylinder serves as an impression cylinder for the other, resulting in simultaneous printing on both sides of the web of paper.
Continuous offset printing is adversely affected by dust and lint from the web of paper which tend to accumulate on the blanket cylinder(s). This dust and lint reduces the quality of the printed product. The accumulation of dust, lint or ink on a blanket cylinder thus presents a serious annoyance and necessitates undesirable down-time for cleaning. The problem is especially acute in the newspaper industry, when, in response to the rising cost of newsprint stock, less expensive grades of paper having higher lint content often are substituted for more expensive grades.
Previously known vacuum devices for cleaning blanket cylinders involved wet vacuum systems for removing debris. In these systems, segments of the blanket cylinder are continually immersed and cleaned with a solvent. The excess solvent is then removed by a wiper with a vacuum header adjacent the wiper blade. See, for example, U.S. Pat. No. 3,835,779 to Ross et al. The present invention avoids the need for solvents by employing a completely dry system for removing debris and, unlike previous dry systems, no lint catcher is needed or used.
Additionally, the present invention employs a separate vacuum means unlike the IBM Technical Disclosure Bulletin, "Cleaner to Developer Toner Recirculation", Eide and Witte, Vol. 21, No. 5, October, 1987, pp 359-360 that discloses only a slight vacuum caused by the rotation of the brush.
Lastly, this invention uses the seals to increase the effectiveness of the vacuum means, unlike the Xerox Disclosure Journal, "Flexible Cleaner Seal", McCarroll, Vol. 8, No. 5 September/October 1983, p. 431 which discloses a flexible seal to prevent dirt from escaping into other machine parts.